This invention relates in general to wire or wireless communications networks, such as, digital cellular mobile radio system networks, and more particularly, to intercepting communications of cellular phone target users and routing the information to a dedicated phone number for monitoring the call.
In order to present a complete example, a digital wireless network using cellular technology is described. The invention is not limited to wireless or cellular networks, but could be used in any network where the subscriber identity module (SIM) xe2x80x9csmart cardxe2x80x9d, or similar plug-in SIM provides the digital cellular telephone with an identity. The SIM is a smart card and has a computer and memory chip permanently installed in a plastic card the size of a credit card. The SIM has to be inserted into a reader in a digital cellular telephone before the mobile terminal can be used for its intended routine purposes. A small version of the SIM, called the plug-in SIM may be used for very small hand-portable phones. Certain subscriber information is stored on the SIM card, together with personal data used by a subscriber, such as personnel phone numbers. The SIM card operates to identify the subscriber to the network. Since only the SIM can personalize a phone, it is possible to travel abroad, taking only the SIM card, and rent a mobile phone at the destination.
One of the pieces of important information which identify a user is the international mobile subscriber number (IMSI) which is permanently stored on the SIM card.
Security Parameters and Authentication
An authentication procedure checks the validity of subscribers"" SIM cards and permits the access to the cellular network. The authentication is based on an authentication algorithm, A3, which is stored on the SIM card. The A3 algorithm uses two parameters: one is the authentication key, Ki, which is stored only on the SIM card and the network. The second value, the randomly generated number (RAND), is transmitted by the mobile station over the air (i.e. via Um interface). Each call setup or registration uses different sets of RAND numbers. One important point of this security feature is that the relevant parameters A3 and Ki are stored in secured places and are never transmitted over the air.
To protect signaling and user data, digital cellular phone systems use a ciphering method, or ciphering algorithm, which is caller A5/1. The algorithms require a random generating specific key, Kc which is delivered from the network. This is the same number that was used for the authentication procedure. The only difference is that algorithm, A8, is used to produce the Kc. The designer of the ciphering aspects claim that this algorithm is so well protected against eavesdropping that even if someone knows the complete specifications, it is very difficult to intercept the information. This, of course, means that law enforcement agencies or other organizations which may need to listen in on private mobile phone conversation in the past, are no longer able to do so.
To protect users from possible intruders a temporary identity is assigned to all subscribers. This identity (TMSI) is stored along with the real identity (IMSI) in the network. The temporary identity is assigned during the location updating procedure, and is used as long as a subscriber remains active in the network. The mobile station uses TMSI to originate the call and the cellular network uses TMSI to page the mobile station. This means the mobile identity TMSI is changed every session of the mobile station, making it even more difficult to monitor digital cell communications.
It is an object of the instant invention to provide for law enforcement agencies a xe2x80x9cdigital wiretapxe2x80x9d which is required by Communication Assistance for Law Enforcement Agency (CALEA).
It is also an object of the instant invention to offer a substantially fully meshed system comprising control networking having a plurality of activator devices and correspondent SIM card in the mobile station.
It is another object of the instant invention to provide xe2x80x9cdigital wiretapxe2x80x9d for target mobile users and that operates completely independent of the polling, roaming schemes, and A3, A5, and A8 algorithms.
It is a further object of the instant invention to provide an activation/deactivation of target phone users by an activator apparatus that transmits short messages including subscriber ID and target phone numbers and that reaches out and finds the target phone.
It is yet another object of the instant invention to provide storing the short message with predetermined phone number/numbers in the SIM card that allows one to modify target phone calls as a xe2x80x9cconference callxe2x80x9d.
It is yet further object of the instant invention to provide activation/deactivation of the target phone by using A-interface (off the switch) or Um- interface (off the air).
The objects of the instant invention are accomplished by a CALEA system comprising a short message which works in conjunction with existing physical mobile network. The short message of the instant invention works in conjunction with and is compatible with existing physical networks. The physical mobile networks is a regular networks provide the actual communication links between and users- cellular phone subscribers whether it be airlinks, or direct wireline links though MSC or PSTN or other communication connection system.
The Activator system (by using a subscriber data base) performs location, initiates communication (by sending a short message) links between Activator and target phone and activates or deactivates the target phone. A SIM card stores predetermined phone number/numbers in the memory. After that every incoming or outgoing call will be modified as a xe2x80x9cconference callxe2x80x9d with a predetermined phone number corresponding to a law enforcement listening room.
Thus, there is disclosed a system for interception of digital cellular phone communications which is required by Communication Assistance for Law Enforcement Agency CALEA. The system includes a plurality of wide area networks which control the transmission of voice, data, file and other types of messages in a reconfigured exchange area, each area network including at least one air interface Base Station (BS) controlled by a central regional service point Mobile Switch Center (MSC) which is connected to an Activator system. The Activator system is a computer based system controlled by a microprocessor and having a database for permanently and temporarily storing predetermined cellular phone subscriber information and messages from and intendant for selected end users. Activators communicate with each other and with other wide area network via a physical communication network which provides communication links between the networks and the end users, whether wireless or wired.